(1) Field of the Invention
The present invention relates to a process for preparing an image-bearing plate, and particularly to a process suitable for use in preparing lithographic printing plates, color proofing sheets, picture plates for overhead projecters, integral circuits, photomasks or the like.
(2) Description of the Prior Art
In preparing a lithographic printing plate, photoresist or the like, there has been widely used an O-quinone diazide compound as a positive working light-sensitive substance. Such O-quinone diazide compounds are described in a number of publications including U.S. Pat. Nos. 2,766,118 and 2,767,092.
An O-quinone diazide compound decomposes, upon irradiation with actinic rays, to produce a carboxylic acid having a five-membered ring, to thereby become alkali-soluble so that they have been used as a light-sensitive substance. However, they have a drawback in that the light-sensitivity is insufficient. The drawback comes from the fact that, when an O-quinone diazide compound is irradiated with actinic rays, the quantum efficiency does not exceed one.
There have been proposed a variety of methods for increasing the light-sensitivity of compositions containing O-quinone diazide compounds, for example, as described in U.S. Pat. Nos. 3,661,582; 4,009,003, and 4,307,173. However, it is found that even by such methods the light-sensitivity is increased only two or three times higher than the conventional composition containing O-quinone diazide compounds.
It has also been proposed to use, as a positive working light-sensitive substance, compounds other than O-quinone diazide compounds. For example, in U.S. Pat. No. 3,849,137 there is proposed the use of polymeric compounds having ortho-nitrocarbinol ester groups. However, the light-sensitivity of such compound is not satisfactory, for the same reasons as in O-quinone diazide compounds.
Another approach to obtain an increased light-sensitivity is utilization of a compound capable of producing an acid through photolysis, in which the acid produced by the photolysis causes a second reaction leading to the solubilization of the exposed area. Thus, there have been proposed various light-sensitive systems comprising such compound capable of producing an acid by photolysis in combination with, for example, an acetal or ortho-N-acetal compound as in U.S. Pat. No. 3,779,778; an orthoester or amidacetal compound as in U.S. Pat. No. 4,101,323; a polymeric compound having acetal or ketal groups at the main chain thereof as in U.S. Pat. No. 4,247,611; an enolether compound as in U.S. Pat. No. 4,248,957; N-acyl iminocarbonate compound as in U.S. Pat. No. 4,250,247; or a polymeric compound having orthoester groups at the main chain thereof as in Japanese patent application (OPI) No. 17345/1981. The term "OPI" used herein means a published unexamined application. These systems exhibit higher light-sensitivity since the photoreaction will theoretically take place with a quantum efficiency exceeding one.
However, the use of a light-sensitive composition comprising such compound capable of producing an acid through photolysis is disadvantageous in that it results in a troublesome problem which is known as "latent-image sensitization". More specifically, the decomposition reaction for solubilizing the exposed area will progressively take place, due to the acid produced, even after the exposure so that it will take as long as one hour or more before attaining of a desired steady sensitivity. That is, the longer the interval between the exposure and the development, the higher the sensitivity becomes. Thus, there is observed a remarkable difference in sensitivity between a case where a light-sensitive plate is developed immediately after the imagewise exposure and a case where a number of light-sensitive plates are successively imagewise exposed and stacked, and then, after certain periods of time, subjected to a development operation.
There has also been proposed a process for increasing the sensitivity of such light-sensitive plates through heating before, during and/or after the exposure, for example, by contacting the plate with a heated roll, by hot air or irradiation with infrared rays, as described in Japanese patent applications (OPI) Nos. 114031/1983 and 119343/1982. It is, however, difficult, by such methods, to constantly obtain a desired steady sensitivity.